Glucan, a neutral B-1,3 polyglucose derived from the cell wall of Saccharomyces cerevisiae, has been demonstrated by our Laboratory to be a potent macrophage and immune stimulant and inhibitor of malignant tumor growth and metastases in a variety of experimental models. Glucan has also been demonstrated to possess the capability of modifying an extensive array of bacterial, fungal, and viral diseases in experimental animals and to function as an adjuvant in the induction of immunicity to tumor cells, virus and parasite antigens. In view of the potential application of glucan as an immunotherapeutic agent, soluble fractions will be prepared from glucan and evaluated for anti-tumor, anti-bacterial and anti-viral activity. The solubilization of glucan is anticipated to eliminate problems inherent in the use of particulate insoluble materials. The employment of soluble, defined molecular entitites in a continued evaluation of immunobiological activities of glucan and its mechanism of action is anticipated to advance the appreciation of its immunotherapeutic potential.